Can't send or receive MMS messages

@beyondplt thank you so much, I kept checking that but never checked the settings within that apn. A quick Google search of at&t APN and I found this

what's your software version? does it end with UCF? it's in the software info

download samsung members app from the galaxy store and submit an error report there

UCB, the update from 4/12

Good morning @ABCD123459,

Thank you for reaching out to us. 

We would be more than happy to investigate your issue regarding being unable to send text messages and encountering network errors.

We can certainly understand how frustrating this must be in the mean time, and we want to ensure we are getting to the bottom of the issue. To aid us in our investigation, please may you verify and answer the following questions:

• Have you completed all steps from our Troubleshoot and Resolve page? ( If you have already gone through this, no worries we will move forward.)
• Have you recently switched from an iPhone to an Android device prior to this issue
• Have you factory reset your device?
• Have you tried taking out the sim card and making sure it is secure within the sim card tray? This link will show how to do this step
• Are you able to make and receive phone calls?

If there are any other issues you are encountering on your device, please let us know. We are also happy to answer all additional questions and concerns. 

Thank you for being a part of our AT&T family. We look forward to hearing from you soon. 

- Amber AT&T Community Specialist 

I have this exact problem also. Talked with AT&T yesterday and did the troubleshooting to no avail. 

Items tried: rebooting, reset network settings, turn off wifi, cleared device cache, cleared messaging app cache, confirmed APN settings, AT&T sent new provisioning

Samsung Note 20 Ultra unlocked, firmware ending in UCB which was installed on 4/13 and all MMS capability ended. 

@wh876kjdlid32 were you texting with iPhone users? or Android users? which carrier do they use? 

"were you texting with iPhone users? or Android users? which carrier do they use?"

Hi ,@beyondplt  Yes a mixture of Android and iPhone users. A lot of them use AT&T. I don't know what everyone of them use. 

This is not a cross network or cross device issue. Unable to send or receive MMS from my wife's phone which is a unlocked Samsung S20 Ultra and on the same AT&T account.  She can send/receive MMS just fine from anyone else. 

The issue is between my phone and the MMS gateway. If I try to send anything MMS (picture, gif, multiple people) it gets stuck "sending" and never completes. If someone sends me a MMS, I get a "there's a new MMS click to download". I click, the icon spins, and it never downloads. 

@beyondplt same as the other poster, unlocked note 20 ultra, group and single mms with Android and iPhone users with either AT&T or Verizon. My husband has no issues with the exact same phone.

@ATTHelp tried all of those things and also have spent HOURS on the phone and chat with AT&T. yesterday they finally admitted that it's a known issue still no resolution